The present invention generally relates to avionics electronics. More specifically, the present invention relates to methods and devices for providing altitude alert and density altitude features within transponders.
A variety of transponders exist today for use with the Air Traffic Control Radar Beacon System (ATCRBS) and that support various communications protocols, such as Mode-C, Mode-A and Mode-S communication's protocols. ATCRBS ground stations, each have a rotating radar dish that transmits a beam having directional characteristics to transmit and receive information to and from aircraft within the relevant air space. The radar dish transmits over a common frequency to all of the aircraft. Each ATCRBS ground station also includes an omnidirectional antenna co-located with the directional radar dish. The omnidirectional antenna transmits, over a control frequency, among other things, side lobe suppression (SLS) signals which, as explained below in more detail, are synchronized to, and used in combination with, transmissions over the common frequency from the directional radar dish. The SLS signals are utilized to prevent aircraft outside of the beam from replying to transmissions generated by the directional radar dish. The aircraft transponders compare certain pulses transmitted from the radar dish over the common frequency with certain pulses transmitted from the omnidirectional antenna over the control frequency. The aircraft transponder determines whether to reply to received signals depending upon the relation between the compared pulses.
However, existing transponders have met with certain limitations. For example, existing transponders do not provide a pilot with altitude data nor density altitude data. Density altitude is an altitude that is an estimate of an aircraft's expected performance based on atmospheric conditions. For example, atmospheric conditions may cause an aircraft flying at 7000 feet to experience flight conditions as if it were flying at 8500 feet under standard atmospheric conditions.
A need remains for an improved transponder able to provide additional data to a pilot or crew to help to avoid aircraft accidents associated with altitude and density altitude. It is an object of certain embodiments of the present invention to meet one or more of these needs and to meet other needs that will become apparent from the present application.